Automatic mechanical transmissions are well known and widely used, especially in heavy duty vehicles. An example of a prior art transmission of this type is shown in U.S. Pat. No. 4,860,861 to Gausch et al. which is incorporated by reference herein.
To facilitate an understanding of the present invention, it is helpful to briefly review the operation of a commercially available automatic mechanical transmission, particularly the type sold by Eaton Corporation, the assignee of the present invention. The basic Eaton automatic mechanical transmission is schematically illustrated in FIG. 1 of the present application and described in detail in U.S. Pat. No. 4,860,861 and the references cited therein. The automatic mechanical transmission is made up of two main components, a torque converter assembly and a mechanical transmission. The torque converter assembly operatively connects the engine crankshaft to the mechanical transmission. The mechanical transmission has an output shaft connected to the vehicle drivetrain.
The torque converter assembly includes a conventional torque converter, a lock-up clutch and an interrupt clutch. When the lock-up clutch is engaged, the torque converter is inoperative and power is transmitted directly through the torque converter assembly. When the interrupt clutch is disengaged, the engine is decoupled from the mechanical transmission. The present invention relates to a piston return mechanism and a lubrication system for the interrupt clutch.
The prior art transmission illustrated in the U.S. Pat. No. 4,860,861 patent utilizes a simple mechanism for reducing the flow of lubricant when the interrupt clutch is disengaged. A lubricant passageway formed in the driven clutch member provides a flow of pressurized lubricant to the clutch element. When the clutch is fully disengaged and the piston retracted, the piston spring blocks the lubricant passageway. When the piston is moved off of the fully retracted position, lubricant flows through the passageway. This mechanism is described in detail in the U.S. Pat. No. 4,860,861 patent in column 1, line 51 et seq. and the related drawings.